for_each_process_thread() is sub-optimal. All threads share the same
->mm, we can swicth to the next process once we found a thread with
->mm != NULL and ->mm != mm.

Signed-off-by: Oleg Nesterov <o...@redhat.com>
Reviewed-by: Michal Hocko <mho...@suse.cz>
---
 kernel/exit.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index e270d2a..429659c 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -358,9 +358,15 @@ retry:
        /*
         * Search through everything else, we should not get here often.
         */
-       for_each_process_thread(g, c) {
-               if (!(c->flags & PF_KTHREAD) && c->mm == mm)
-                       goto assign_new_owner;
+       for_each_process(g) {
+               if (g->flags & PF_KTHREAD)
+                       continue;
+               for_each_thread(g, c) {
+                       if (c->mm == mm)
+                               goto assign_new_owner;
+                       if (c->mm)
+                               break;
+               }
        }
        read_unlock(&tasklist_lock);
        /*
-- 
1.5.5.1

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